1. Field of the Invention
The present invention relates to a magnetic video reproducing apparatus. More specifically, the present invention relates to an improvement in a magnetic video reproducing apparatus for reduction of noise occurring on a monitoring picture on the occasion of high speed reproduction.
2. Description of the Prior Art
A magnetic video tape recording/reproducing apparatus for home use so far proposed and put into practical use typically employs a rotational two-head system, a helical scan system and an azimuth system. By a rotational two-head system is typically meant a system in which two video heads are provided at the directly opposite positions on the circumference of a rotating drum spaced apart by 180.degree. from each other. By a helical scan system is typically meant a system in which a magnetic tape is made to travel in an oblique direction with respect to the rotational direction of the video heads. By an azimuth system is typically meant a system in which the gap directions of the above described two heads are each afforded a different angle so that the corresponding directions on the recorded tracks recorded by the above described two heads on a magnetic tape may be different and hence may intersect each other. The above described rotational two-head system, helical scan system and azimuth system have been fully described in, for example, U.S. Pat. No. 3,925,810 issued Dec. 9, 1975 to Yoshio Ishigaki et al; U.S. Pat. No. 3,812,523 issued May 21, 1974 to Hisaaki Narahara; U.S. Pat. No. 4,012,771 issued Mar. 15, 1977 to Yoshio Ishigaki et al; U.S. Pat. No. 3,918,085 issued Nov. 4, 1975 to Toshihiko Numakura et al, and U.S. Pat. No. 4,079,412 issued Mar. 14, 1978 to Yoshiteru Kosaka.
Since the above described three systems constitute the background of the present invention, an outline of these three systems will be briefly described to the extent necessary for description of the present invention.
FIG. 1 is a diagrammatic view showing the rotational two-head system. Two video heads Ha and Hb are provided on the circumference of a rotational drum 1 at the directly opposite positions spaced apart by 180.degree. from each other. Since the rotational drum 1 is caused to be rotated at a high speed, say 1,800 rpm, in the arrow direction as viewed in FIG. 1, the two video heads Ha and Hb are correspondingly rotated at a high speed. A magnetic tape 2 is set around the rotational drum 1 to be in an .OMEGA. shape to extend along more than a half of the circumference. The magnetic tape 2 is pinched between a capstan 3 and a pinch roller 4 so that the tape 2 may be made to travel by means of the capstan 3. For convenience of description of the operation, it is now assumed that the travel of the magnetic tape 2 in the solid line arrow direction is referred to as "winding" and the travel of the magnetic tape 2 in the dotted line arrow direction is referred to as "rewinding".
FIG. 2 is a diagrammatic view showing a helical scan system. The magnetic tape 2 is fed around the circumference of the rotational drum 1 in an oblique direction with respect to the axial direction of the rotational drum 1. Accordingly, it follows that the video heads Ha and Hb rotate in an oblique direction with respect to the travel direction of the magnetic tape 2. Therefore, the video heads Ha and Hb trace the magnetic tape 2 in the corresponding oblique direction. The rotational drum 1 is rotatably provided on a fixed cylindrical drum 6 having the same diameter as the rotational drum 1 with a small slit 5 between the rotational drum 1 and the fixed cylindrical drum 6.
FIGS. 3A and 3B are diagrammatic views showing an azimuth system. The video heads Ha and Hb each have gaps Ga and Gb, respectively, and are adapted to be rotated and hence to move in the arrow direction as viewed in FIGS. 3A and 3B. The gaps Ga and Gb of the heads Ha and Hb, respectively, are formed with a small oblique angle .theta. but in the opposite directions with respect to the direction normal to the rotational direction. The above described small oblique angle .theta. is referred to as an azimuth angle and is typically selected to be say 6.degree.. As to be more fully described subsequently, the azimuth system is employed to reduce a cross talk. The width of each of these video heads Ha and Hb is denoted by the character W.
A typical video tape recording/reproducing apparatus for home use so far proposed and put into practical use is typically designed to have three recording/reproduction modes, which are referred to as a standard play mode, a long play mode, and an extended play mode. The standard play mode is adapted to perform recording/reproduction of one standard magnetic tape for two hours. The long play mode is adapted to perform recording/reproduction of one standard magnetic tape for a period of time as long as two times that of the standard play mode. The extended play mode is adapted to perform recording/reproduction of one standard magnetic tape for a period of time as long as three times that of the standard play mode. Since the differences of the long play mode and the extended play mode are similar to each other, except for a difference in a recording/reproduction time period of two times in the long play mode and three times in the extended play mode, only the standard play mode and the extended play mode will be described in the following for facility of description.
FIG. 4 is a diagrammatic view showing a pattern of recorded tracks as viewed from the standpoint of a magnetic aspect generated in recording of the standard play mode. It is to be pointed out that the tape patterns shown in the tape pattern diagrams of the present application are all similarly illustrated from the magnetic aspect. As seen from FIG. 4, the magnetic tape 2 includes video tracks Ta and Tb, a control track Tc and an audio track, (not shown), for simplicity of illustration. On the occasion of recording and reproduction, the magnetic tape 2 is taken or wound in the direction of the arrow TS at a constant speed of say 33.35 mm/s. Since the above described helical scan system is employed, the video heads Ha and Hb are rotated or moved in the direction as shown by the arrow HS obliquely by a predetermined angle with respect to the tape traveling direction. On the occasion of recording, a video signal is recorded on the video tracks Ta and Tb by means of the video heads Ha and Hb, respectively, and on the occasion of reproduction the video signal thus recorded is reproduced by means of the respective video heads while the same trace the above described video tracks Ta and Tb. Thus, it follows that the video tracks Ta and Tb are formed with an oblique angle .alpha.1 with respect to the tape traveling direction. Although the angle .alpha.1 was illustrated as if it were considerably large for facility of depiction, in actuality the angle .alpha.1 is as extremely small as approximately 5.degree.59'. The video tracks Ta and Tb each represent one odd numbered field and one even numbered field of a television picture. As well-known a composition of the odd numbered field and the even numbered field constitute one frame. A video tape recording/reproducing apparatus without employing an azimuth system needs formation of a guard band having no video signal recorded between the adjacent video tracks Ta and Tb for the purpose of eliminating a cross talk between the adjacent video tracks Ta and Tb. However, employment of the azimuth system eliminates necessity of forming a guard band and makes it possible to record a video signal in the video tracks Ta and Tb without a guard band therebetween by eliminating a problem of cross talk therebetween. More specifically, in the case of the azimuth system where no guard band is formed, even if one video head, say Ha traced the adjacent video track, say Tb, a video signal is little reproduced from the adjacent video track, say Tb due to the above described difference between the gap angles for recording. Such loss of a video signal being reproduced from the adjacent video track is referred to as an azimuth loss and such azimuth loss is as large as approximately -40 dB for a video signal of 4 MHz, for example, which means that employment of the azimuth system without a guard band considerably reduces a cross talk. In performing the standard play mode, usually video heads particularly designed for a standard play mode are used. Assuming that the width of each of the video heads designed for a standard play mode is W1, say 58 .mu.m, then the width of each video track accordingly becomes W1. Since there is no gap between the adjacent video tracks, the pitch P1 of the video tracks also becomes equal to W1. Meanwhile, in actual video tape recording/reproducing apparatuses the width of these two video heads is selected to be slightly larger than the width of the video tracks for the purpose of slow reproduction, still reproduction and the like and furthermore the width value of each of the two video heads is selected to be different from each other. For example, in the case where the width of the video tracks is selected to be 58 .mu.m, the width of the video head Ha is selected to be 70 .mu.m and the width of the video head Hb is selected to be 90 .mu.m. However, for facility of description, now it is assumed that the width of each video head is selected to be equal to each other and is selected to be 58 .mu.m. It is pointed out that the above described assumption does not make any difference in description of the operation principle. Typically, the control track Tc is adapted to have a control pulse Cp recorded for the purpose of rotational phase control of the rotational drum 1 and travel phase control of the magnetic tape 2. The control pulse Cp is a pulse signal of say 30 Hz. Assuming that the traveling speed of the magnetic tape is 33.35 mm/s, the interval of the adjacent control pulses would be approximately 1.11 mm.
FIG. 5 is a diagrammatic view of a tape pattern recorded in the extended play mode. Now only a different point of the FIG. 5 tape pattern from the FIG. 4 tape pattern will be described. The magnetic tape 2 is wound in the direction of the arrow TS at a predetermined speed, say 11.12 mm/s which is as small as one-third of that of the standard play mode. The rotational speed of the video heads Ha and Hb remains the same as that in the standard play mode. Accordingly, the angle .alpha.2 of the video tracks Ta and Tb with respect to the tape traveling direction becomes different from the angle .alpha.1 attained in the standard play mode. However, since such difference in angle is extremely small, in the following the operation is considered on the assumption that there is no difference in the angle between the standard play mode and the extended play mode. In the extended play mode the video heads particularly designed for an extended play mode are used. The width W2 of the video heads for use in the extended play mode is selected to be as small as say 19.3 .mu.m and one-third of the width W1 of the video heads for use in the standard play mode. Accordingly, the width W2 of the video tracks would become one-third of the width W1. Since there are no gaps between the adjacent video tracks, as described previously, it follows that the pitch P2 of the video tracks also becomes equal to the width W2. The control pulse Cp in the extended play mode is the same as that in the standard play mode and is a pulse signal of 30 Hz. Accordingly, assuming that the traveling speed of the magnetic tape is 11.12 mm/s, the interval of the adjacent pulses as recorded would be approximately 0.37 mm.
In the foregoing the standard play mode and the extended play mode of a typical magnetic video recording/reproducing apparatus were described. Now the respective features of both modes will be briefly described. Generally speaking, in the standard play mode the width of the video tracks is broader and the quality of the reproduced picture is better but the tape traveling speed is large and the time for recording and reproduction of one standard tape becomes short and hence the standard play mode is less economical. On the other hand, in the extended play mode the tape traveling speed is small and the recording/reproducing time period is prolonged and thus the extended play mode is more economical, although the width of the video tracks becomes small and hence the picture quality becomes less good.
In actually using such a magnetic video recording/reproducing apparatus, some users prefer a better picture quality at the sacrifice of a shortened recording/reproducing time and hence of less economy, whereas conversely other users prefer a prolonged recording/reproducing time and hence more economy at the sacrifice of a less good picture quality. However, it is not economical to provide two magnetic video recording/reproducing apparatuses one particularly designed for a standard play mode and the other particularly designed for an extended play mode. Thus, it is desired that a magnetic video recording/reproducing apparatus capable of performing both a standard play mode and an extended play mode is provided.
One approach to realize the above described desire of a magnetic video recording/reproducing apparatus capable of performing both a standard play mode and an extended play mode is to employ rotational four heads in a rotational head assembly, one pair of heads being particularly designed for a standard play mode and the other pair of heads being particularly designed for an extended play mode. FIG. 6 is a diagrammatic view showing the rotational four heads. One pair of video heads Ha and Hb is disposed on the circumference of the rotational drum 1 at directly opposite positions so as to be spaced apart by 180.degree. from each other and another pair of video heads Ha' and Hb' is also provided on the circumference of the rotational drum 1 so as to be spaced apart by 180.degree. from each other but dislocated by 90.degree. as compared with the previously described pair of heads Ha and Hb. Of these two pairs of video heads, for example the pair of video heads Ha and Hb is particularly designed for a standard play mode, whereas the other pair of video heads Ha' and Hb' is particularly designed for an extended play mode. As a matter of course, one of these pairs of heads is selected in operation. On the occasion of reproduction, for the purpose of automatic selection between these two pairs of heads use may be made of the fact that as described previously the interval of the control pulse Cp in the standard play mode is larger than that in the extended play mode. A tape pattern in the case where a video signal is recorded using the pair of video heads Ha and Hb particularly designed for a standard play mode is as shown in FIG. 4, whereas a tape pattern in the case where a video signal is recorded by the other pair of video heads Ha' and Hb' particularly designed for an extended play mode is as shown in FIG. 5.
Another desire which arises in using such a magnetic video recording/reproducing apparatus is a high speed reproduction mode. By a high speed reproduction mode is typically meant a mode in which reproduction is made of a magnetic tape at a high speed as compared with that of an ordinary reproduction mode, i.e. a mode of reproduction of a magnetic tape at the same speed as that in recording. For simplicity of description, let it be assumed that the ratio of the tape travel speed on the occasion of the high speed reproduction mode to that on the occasion of the normal reproduction mode is referred to as "a speed ratio". The high speed reproduction mode includes a high speed winding reproduction mode in which a magnetic tape is recorded as the same is wound and a high speed rewinding reproduction mode in which a magnetic tape is reproduced as the same is rewound. Typically a high speed reproduction mode is used for the purpose of quickly looking for a recorded picture, quickly skipping an undesired portion of the recorded picture, such as a picture for advertisement, when a program is recorded from the commercial television broadcasting.
For the purpose of high speed reproduction usually the capstan 3 for causing a magnetic tape 2 to travel is rotated at a high speed. FIG. 7 is a block diagram showing a conventional capstan motor control circuit for high speed reproduction. The above described capstan 3 is mechanically driven by means of a capstan motor 7. The conventional capstan motor control circuit for high speed reproduction comprises a variable resistor 9, a switch 10 and an amplifier 11. One terminal 8 out of fixed terminals of the variable resistor 9 is supplied with a direct current voltage of an approximately constant voltage, while the other terminal is connected to the ground. A movable terminal of the variable resistor 9 is connected to a contact g of the switch 10. The contact f of the switch 10 is connected to a servo circuit, not shown, for the purpose of the ordinary reproduction mode. A common contact e of the switch 10 is connected to the input of an amplifier 11 and the output of the amplifier 11 is connected to the above described capstan motor 7. On the occasion of the high speed reproduction, the common contact e of the switch 10 is turned to the contact g, whereby the capstan motor 7 is supplied with a high voltage so that the capstan motor 7 is rotated at a high speed. Accordingly, the magnetic tape 2 is also caused to travel at the high speed. If it is desired to change the travel speed of the magnetic tape 2, the variable resistor 9 is adjusted.
The conventional capstan motor control circuit for high speed reproduction is structured as described above and the speed ratio in the high speed reproduction is not accurately controlled to be several times the speed of the normal reproduction mode but is determined roughly to be approximately 9 to 10 times the speed of the ordinary reproduction mode. Such multiple number is very roughly determined to be approximately 9 to 10 in consideration of the desire of the users of a magnetic video recording/reproducing apparatus.
Now description will be made of how a picture appears on the screen when high speed reproduction is made using the above described conventional capstan motor control circuit for high speed reproduction. Since the speed ratio is determined very roughly as described previously, for simplicity of description it is considered how a picture appears on the screen when high speed reproduction is made at the speed as large as approximately 9.5 times the speed of the normal reproduction mode. Further, for facility of illustration, consider a case where a magnetic tape having a video signal recorded in the extended play mode is reproduced in a high speed winding reproduction mode.
FIG. 8 is a diagrammatic view showing loci of the video heads in the case where a magnetic tape having a video signal recorded in an extended play mode is reproduced in a high speed winding reproduction mode at the speed as large as 9.5 times the recording speed, i.e. at the speed ratio of 9.5. For simplicity of illustration, patterns of such a control tracks unnecessary for depiction will be omitted in illustration. In the figure, the arrow TS denotes a tape travel direction, the arrow HSa denotes a rotational direction of the video head Ha' and the arrow HSb denotes a rotational direction of the video head Hb'. As described previously, video tracks Ta1, Tb1, Ta2, Tb2, . . . are formed on the tape surface. The video tracks Ta1, Ta2, . . . are formed by the video head Ha', whereas the video tracks Tb1, Tb2, . . . are formed by the video head Hb'. Now let it be assumed that the video head Ha' starts tracing from the lower end a of the video track Ta1. If and when the speed ratio is unity which means the apparatus is in the ordinary reproduction mode, the video head Ha' traces the video track Ta1 to reach the upper end a' of the video track Ta1. However, since it was assumed that the speed ratio is 9.5, the video head Ha' comes to the upper end a" shown at the upper end of the magnetic tape in FIG. 8, i.e. a point spaced apart from the upper end a' in the direction opposite to the tape travel direction by 9.5 video tracks counting from the track of the upper end a'. The locus TRa of the video head Ha' in such situation is shown by the dotted lines. While the video head Ha traces the tape from the lower end a to the upper end a", only a video signal recorded in the video track Ta is picked up due to the previously described azimuth loss as to the video track Tb. The portion where a video track is picked up on the locus TRa has been hatched. In the case where the speed ratio is the unity, the video head Hb' starts tracing the tape from the lower end b of the video track Tb1. However, since it was assumed that the speed ratio is 9.5, the video head Hb starts tracing the tape from the lower end b', i.e. a point spaced apart by 9.5 video tracks in the direction opposite to the tape traveling direction counting from the video track of the lower end b. As in the case of the video head Ha', the video head Hb' then reaches the upper end b". The locus TRb of the video head Hb' in such situation is shown by the dotted lines. As the video head Hb' traces the video tracks from the lower end b' to the upper end b", as in the case of the video head Ha', only a video signal recorded on the video tracks Tb is picked up due to the azimuth loss as to the video tracks Ta. The portion where the video signal is picked up on the locus TRb has been hatched. In the foregoing the speed ratio of 9.5 was taken only by way of an example. However, as described previously, as a matter of practice the speed ratio cannot be determined precisely to be 9.5 and hence the speed ratio could fluctuate approximately 9 to 10, for example. It would be readily appreciated from the foregoing description that in such a case the spacing between the loci TRa and TRb and the inclination of both loci could change accordingly.
Now description will be made of a picture appearing on the screen in the case where the video heads Ha' and Hb' trace the magnetic tape as described in the foregoing. FIGS. 9A and 9B each show a picture of one field formed by tracing of the respective video heads Ha' and Hb'. FIG. 9C shows a picture of one frame composed with the pictures of both fields. Referring to FIG. 9A, the points a and a" correspond to the points a and a" in FIG. 8, respectively. While the video head is picking up a video signal, a picture portion P appears on the screen and otherwise a noise band N appears on the screen. Meanwhile, for the purpose of reducing any visual interference caused by such noise bands, one might think of an approach to darken corresponding portion on the screen if and when the video head is not picking any video signal. However, such an approach is not successful due to the face that a flickering phenomenon becomes to remarkable to cause users to feel too uncomfortable to make the approach useless. Accordingly, without such approach, it follows that the picture portion P and the noise bands N appear at alternate positions on the screen. The same as FIG. 9A applies to FIG. 9B. However, as is apparent from FIG. 8, the positions of the noise bands N have been slightly dislocated as compared with those in the case of FIG. 9A. Accordingly, the picture shown in FIG. 9C showing a picture of one frame includes the noise bands N the number of which is two times that which appears in FIGS. 9A and 9B. According to the actual experimentation, it has been observed that the noise bands N on the screen are thin stripe patterns which move upward and downward while the number of the stripes increases and decreases. The reason is that some times the noise bands in FIG. 9A and the noise bands N in FIG. 9B come to be overlapped as shown in FIG. 9A and some other times the noise bands N in FIG. 9A and the noise bands in FIG. 9B are dislocated so that the noise band patterns come to appear as shown in FIG. 9C. In spite of such noise bands, a picture itself can be fully observed and as the result the function of the high speed reproduction can be fully achieved.
In the foregoing, a description was made of the case where the magnetic tape having a video signal recorded in an extended play mode is reproduced in a high speed winding reproduction mode. However, substantially the same occurs also in reproduction in a high speed rewinding reproduction mode. Substantially the same also applies to a case where a magnetic tape having a video signal recorded in a standard play mode is reproduced in a high speed winding reproduction mode or a high speed rewinding reproduction mode.
As is fully appreciated from the foregoing description, a magnetic video recording/reproducing apparatus employing a rotational four-head system makes it possible to satisfactorily achieve a function of a high speed reproduction in spite of the fact that several thin noise bands appear on the screen while the same are moving upward and downward on the occasion of high speed reproduction. Nevertheless, employment of a rotational four-head system in a magnetic video recording/reproducing apparatus for home use involves two major serious problems. One is a problem of economy. More specifically, video heads are one of most expensive components in a magnetic video recording/reproducing apparatus and provision of two pairs of video heads on a rotational drum requires an extremely severe precision. Thus, provision of these two pairs of video heads causes an increase of a cost commensurate with one additional pair of heads per se, an increase of a cost commensurate with a video head selecting circuit for selection among these two pairs of video heads, and an increase of a cost required or work of providing one additional pair of heads onto a rotational drum, totaling an increase by several percents of the total costs of a magnetic video recoding/reproducing apparatus. The other problem is wear of a magnetic tape. More specifically, in the case of a rotational four-heads, a magnetic tape is worn by the heads two times faster than the wear which occurs in the case of the rotational two-head system.
In order to evade the above described problems, a magnetic video recording/reproducing apparatus capable of performing recording and reproduction both in a standard play mode and extended play mode using the rotational two-head system has been proposed. Such type of a magnetic video recording/reproducing apparatus of a rotational two-head system employs only one pair of video heads, i.e. video heads Ha' and Hb', having a narrow width particularly designed for an extended play mode and is adapted to record and reproduce a video signal in a magnetic tape with a spacing between the adjacent tracks on the occasion of a standard play mode. FIG. 10 is a diagrammatic view showing a tape pattern having a video signal recorded in a standard play mode using the pair of video heads Ha' and Hb' particularly designed for an extended play mode. The width of the video heads designed for an extended play mode is W2, as described previously, and therefore, the width of the video tracks Ta and Tb also become W2 as in the case of an extended play mode (see FIG. 5). On the other hand, since a magnetic tape is caused to travel in a standard play mode, the pitch between the adjacent video tracks becomes P1 as in the case of a standard play mode (see FIG. 4). Otherwise, the remaining matters are the same as those in a standard play mode described previously. Therefore, according to such a magnetic video recording/reproducing apparatus of a rotational two-head system, a non-signal portion is formed between the adjacent video tracks Ta and Tb and such a non-signal portion may be referred to as "a pseudo-guard band G". Meanwhile, in the case where a video signal is recorded in a magnetic tape in an extended play mode using the above described pair of video heads designed for an extended play mode, the tape pattern becomes as shown in FIG. 5, as a matter of course.
Now a description will be made of high speed reproduction by a magnetic video recording/reproducing apparatus capable of recording and reproduction in both a standard play mode and an extended play mode using the above described rotational two-head system. For the previously described reason, it is also assumed that the speed ratio is selected to be 9.5.
Now consider a case where a magnetic tape having a video signal recorded in an extended play mode is reproduced in a high speed reproduction fashion. In such a case the operation is exactly the same as that in the case where the previously described rotational four-head system is employed. More specifically, the loci of the two video heads becomes as shown in FIG. 8 and the pictures appearing on the screen also become as shown in FIS. 9A, 9B and 9C. Accordingly, several lines of noise bands appear on the screen while the same moves upward and downward. Thus, for the previously described reason, a function of high speed reproduction is fully achieved in such a case.
Now a description will be made of a case where a magnetic tape having a video signal recorded in a standard play mode is reproduced in a high speed reproduction fashion. FIGS. 11A and 11B are diagrammatic views showing the loci of the video heads in the case where a magnetic tape having video signal recorded in a standard play mode is reproduced in a high speed winding reproduction fashion at the speed ratio of 9.5. A different point of the pattern shown in FIGS. 11A and 11B from that in FIG. 8 will now be explained. The tape of FIG. 11A and the tape of FIG. 11B are to be connected along the line L-L'. As in the case of FIG. 8, the video head Ha' starts tracing from the lower end a of the video track Ta1 to reach the upper end a". The locus TRa of the video head Ha' at that time is shown by the dotted line. While the video head Ha' traces the tape from the lower end a to the upper end a", only a video signal recorded in the video track Ta is picked up. The portion where a video signal is picked up is shown as hatched on the locus TRa. Similarly the video head Hb' also starts tracing the tape from the lower end b' of the pseudo-guard band G to reach the upper end b". The locus TRb of the video head Hb' is shown by the dotted line. The portion where a video signal is picked up by the video head Hb' is shown as hatched on the locus TRb. As is appreciated from the foregoing, the portion where a video signal is picked up by the video head is narrow as compared with that in the case of FIG. 8. It is pointed out that for convenience of illustration the oblique angle .alpha.1 of the video track has been illustrated in FIGS. 11A and 11B to be larger than the actual case and the portion where a video signal is picked up is observed to be narrow superficially, but in actuality that portion is not so narrow.
Now a picture to appear on the screen in the case where the video heads Ha' and Hb' trace a magnetic tape as described above will be described. FIGS. 12A and 12B are views showing pictures of one field formed when the video heads Ha' and Hb', respectively, trace a magnetic tape. FIGS. 12C and 12D are views showing pictures of one frame attained through composition of the pictures of both fields. Now the difference of the pictures appearing in FIGS. 12A to 12D from those in FIGS. 9A to 9C will be described. Referring to FIG. 12A, picture portions P and noise bands N appear at alternate positions from the upper portion on the screen. Referring to FIGS. 12B, picture portions and noise bands N appear in a manner similar to that in FIG. 12A. However, as is readily seen with reference to FIGS. 11A and 11B, the positions of the noise bands N in FIG. 12B have been considerably dislocated as compared with that in the case of FIG. 12A. As seen from the illustration, the width of the noise bands N in such a case is considerably wide as compared with that of the noise bands shown in FIGS. 9A, 9B and 9C and according to the experimentation it has been observed that the width of these noise bands becomes approximately equal to the width of the picture portions. In addition, as in the case in FIGS. 9A, 9B and 9C, the positions of these noise bands in FIGS. 12A, 12B and 12C move upward and downward and, if and when it happens by chance that the noise bands in FIG. 12A overlap the noise bands in FIG. 12B, a picture pattern as shown in FIG. 12A, for example is seen; however, such overlap rarely occurs, and in most cases the positions of the noise bands in both fields shown in FIGS. 12A and 12B are dislocated to become as shown in FIG. 12C or as shown in FIG. 12D, in which case mostly or only the noise bands appear on the whole screen. In such a case, a function of high speed reproduction can be hardly achieved.
As described in the foregoing, in the case where a magnetic tape having a video signal recorded in a standard play mode using a pair of video heads designed for an extended play mode is reproduced in a high speed reproduction fashion, in most cases the noise bands appear on the whole screen. For this reason no attempt has so far been made to perform high speed reproduction of a magnetic tape having a video signal recorded in a standard play mode using a pair of video heads designed for an extended play mode. Since most of prerecorded video tapes now commercially available have been recorded in a standard play mode using a pair of video heads for a standard play mode, it would be highly advantageous if a magnetic tape having a video signal recorded in a standard play mode can be reproduced in a high speed reproduction fashion using a pair of video heads designed for an extended play mode.